A Geometric Approach to the Analysis of Global Eolian Hydrocarbon Reservoirs: With Analogues From the Wahiba Sands of Oman

Abstract

It is recognized worldwide that eolian rocks can be very good hydrocarbon reservoirs. The “classic tank” eolian reservoir consists of a framework of well-rounded, well sorted quartz sand grains that incorporates little matrix due to removal of fines by wind. The real-world varies greatly, however, from the “classic tank” because most eolian reservoirs consist of a mélange of complex lithofacies derived from process frameworks operating at multiple scales. Practical geometric reservoir models include local and global climate conditions, sources of sand, wind direction and bedform size, accommodation space, and climatic and tectonic factors that create lacunae in sedimentation at various scales. These phenomena are best recognized through the study of dipmeter and core for any particular field; or less happily, after early water breakthrough at the crest of an oil field signals that unswept rock lies between the off-take well and the oil-water contact. At the global scale, climate variability associated, for example, with Permian glacial cyclicity has stamped a resonant cyclicity on rock units of that age in many parts of the world. At basinal scale controls on sedimentation operate through both auto- and allocyclic processes. Regional winds bring sand to the local system where it is reworked. Fluvial avulsion and water table fluctuations among other factors also control reservoir sedimentology and stratigraphy. At the oil field scale, the reservoir characteristics are controlled mainly by facies stacking, associated bounding surfaces, and vertical trends in texture. At the outcrop scale, crossbedding typical of the various dune types is a key driver of reservoir complexity. At the microscopic scale within eolian genetic units, the poroperm properties of individual primary strata will affect recovery factors for an entire field by controlling fluid movement in pore spaces of the reservoir. The Wahiba Sand Sea of Oman provides modern analogues for some of the reservoir styles we have seen globally. Flow models demonstrate the heterogeneity of hydrocarbon sweep that would be produced by various eolian lithofacies preserved on coastal outcrops of the Southeast Wahiba Sands.

AAPG Datapages/Search and Discovery Article #90193 © 2014 Rocky Mountain Section AAPG Annual Meeting, Denver, Colorado, July 20-22, 2014